This invention relates generally to a mercury ionic gas standard generator for use in the continuous emissions monitoring of exhaust flue gas streams. More specifically, the present disclosure relates to the use of a reservoir being coated with an inert silicon-based coating for transporting a volume of an aqueous ionic mercury solution to a liquid mass flow controller and vaporizer for generating a mercury ionic gas standard.
The United States Environmental Protection Agency (EPA) identifies sources of mercury (Hg) emissions in the U.S. to be utility boilers, waste incinerators that burn mercury-containing wastes (municipal and medical), coal-fired industrial boilers and cement kilns that burn coal-based fuels. A particularly significant source of mercury emissions is coal-fired power plants.
To quantify the emissions from a particular source, a continuous emissions monitoring system (CEMS) is employed for mercury. There are three forms of mercury in exhaust flue gas streams of a coal-fired power plant that may be monitored by a CEMS. These forms are gaseous elemental mercury, gaseous oxidized mercury and particulate bound mercury that is either elemental or oxidized, at stack gas temperatures in excess of 200° F.
Current continuous emissions monitoring systems for mercury using a mercuric chloride liquid standard solution use a peristaltic pump for transporting the mercuric chloride to a liquid mass flow controller and vaporizer. These systems are difficult to use as there can be numerous problems such as tube failure with the peristaltic pumps. For example, in many instances the tube of the peristaltic pump can become clogged or blocked, leading to inconsistencies in delivering the mercuric chloride liquid standard solution to the liquid mass flow controller. This can lead to inaccuracies in the measurements as the efficient mixing of mercuric chloride with the carrier gas (e.g., air or nitrogen) can be questionable.
Additionally, the tubing of the peristaltic pump can tear, requiring expensive maintenance. Furthermore, a torn tube can cause wear and tear on the pump motor itself requiring additional maintenance.
As such, there is a need in the art for the development of a reliable and accurate technology capable of measuring the levels of mercury emitted in an exhaust flue gas stream. More specifically, there is a need for an alternative means of transporting the mercuric chloride liquid standard solution to the liquid mass flow controller and vaporizer without utilizing the peristaltic pump. It would be advantageous if the means could lead to improved accuracy in measuring mercury levels and did not require extensive maintenance such as those for systems using the peristaltic pump.